Conventional cancer treatments are sometimes not expected to bring in meaningful survival effects even if they can induce the regression of tumors, because of the persistent proliferation of malignant tumors, the metastasis or recurrence of cancer, and the resistance to anti-tumor agents. These days, it has been suggested that cancer stem cell (hereinafter referred to as “CSC”) is one of the causes of the failure, which is closely involved in the factors such as the persistent proliferation of malignant tumor. CSCs have been identified in almost all types of major cancers in human such as breast cancer, colon cancer, lung cancer, and hematological malignancy (Non-Patent Document 1). Also, CSCs can be greatly different in the biological feature from normal cancer cells which differentiate from CSCs, and thus the development of an anti-tumor agent whose target is CSCs is expected to lead to a new strategy for cancer treatments (Non-Patent Document 2).
One of the features in CSCs is the self-renewal ability (Non-Patent Document 3). Reliable methods established for measuring the self-renewal ability of cells include, for example, a method for measuring the sphere-forming ability of cancer cells in non-adherent condition in the absence of serum (Non-Patent Document 4).
Non-Patent Document 5 discloses that PF-03084014 having an N-imidazolylamide scaffold can inhibit CSCs to exhibit an anti-cancer effect. However, Non-Patent Document 5 does not disclose the compound of formula (1′) of the present invention.